It mimics a hormone made in the intestines called GLP-1 (glucagon-like peptide), says William Troy Donahoo, MD. He's a staff physician in the Metabolic-Surgical Weight Management Department, Kaiser Permanente, Denver.

One role of GLP-1 is to tell your brain you’re full, he says.

The medicine works in many ways to help beta cells normalize blood sugars. Beta cells make and release insulin when blood sugar is high. They help those with type 2 diabetes keep their blood sugar normal.

How well does Saxenda work?

Donahoo says he expects a range of weight loss responses to Saxenda, just as he has seen various responses from people on Victoza for their diabetes.

Clinical trials of Saxenda continued for about a year and included about 4,800 patients, with some getting the drug and some a placebo.

"Clinical trials show that [more than] 60% of patients getting a daily 3-milligram injection lost at least 5% of their weight and 31% lost more than 10%," says Osama Hamdy, MD, PhD. He's the medical director of the Obesity Program at Joslin Diabetes Center.

In comparison, 34% of those on placebo lost at least 5% of their body weight, according to the FDA.

"It is not an impressive weight loss for an injectable and expensive medication with a lot of potential side events,” Hamdy says. He also says people generally lose less weight outside of clinical trials.